1. Field of the Invention
The present invention relates to a sheet supplying apparatus that supplies a plurality of recording sheets, one by one, to an image recording portion, and an image recording apparatus including the sheet supplying apparatus and the image recording portion.
2. Discussion of Related Art
There is known a sheet supplying device for use in, e.g., an ink-jet recording apparatus. The sheet supplying device supplies a plurality of recording sheets, one by one, to an image recording portion of the ink-jet recording apparatus. The sheet supplying device includes an arm member that is connected, at a base end portion thereof, to a frame of the recording apparatus such that the arm member is pivotable about an axis line. The plurality of recording sheets are stacked on each other on a sheet supporting portion such as a bottom plate of a sheet-supply cassette that opens upward. The arm member is biased downward by a biasing force of a spring, and accordingly a sheet-supply roller supported by a free end portion of the arm member is pressed on the uppermost one of the recording sheets. When the sheet-supply roller is rotated, the uppermost recording sheet is moved relative to the remaining recording sheets, so that a leading end of the uppermost sheet engages an inclined sheet-separate plate provided at a downstream-side end of the sheet supporting portion with respect to a direction of moving of recording sheet. Thus, only the uppermost recording sheet is separated from the other recording sheets remaining on the sheet supporting portion, and is supplied to the image recording portion so that the recording sheet is opposed to the same. This sheet supplying device is disclosed by, e.g., Patent Document 1 (Japanese Patent Application Publication No. 2002-249248) or Patent Document 2 (Japanese Patent Application Publication No. 2004-338905 or its corresponding U.S. Patent Application Publication No. 2005-001371).
In addition, Patent Document 2 teaches that an outer circumferential surface of the sheet-supply roller is formed of a material having a high friction coefficient, such as rubber. Moreover, a portion of the sheet supporting portion that is opposed to the outer circumferential surface of the sheet-supply roller is provided with a material having a high friction coefficient. For example, a cork sheet is adhered to that portion of the sheet supporting portion. Thus, when only a few recording sheets remain on the sheet supporting portion, a frictional resistance is applied to the recording sheet or sheets underlying the uppermost recording sheets, so that the underlying sheet or sheets can be prevented from being supplied with the uppermost sheet directly engaged with the outer circumferential surface of the sheet-supply roller. On the other hand, when no recording sheet remains on the sheet supporting portion, the outer circumferential surface of the sheet-supply roller is pressed on an upper surface of the sheet supporting portion. In this state, if the sheet-supply roller is rotated, then the outer circumferential surface of the roller may be worn excessively. If the frictional force is increased excessively, then the sheet-supply roller may be locked so that a driving system that drives the roller may be broken or an electric motor of the driving system may be seized or stuck. To avoid this problem, Patent Document 2 proposes to form, in the upper surface of the sheet supporting portion, a relief hole that prevents the outer circumferential surface of the sheet-supply roller from contacting the sheet supporting portion.
However, the sheet supplying device disclosed by Patent Document 2 suffers the following drawbacks: When only a few recording sheets remain on the sheet supporting portion and each of the recording sheets is thin, the sheet-support roller may be pressed, by the biasing force of the spring to bias the arm member downward, against the recording sheets, so that the recording sheets may be partly forced into the relief hole. Thus, the recording sheets may be flexed, or wrinkled, along the edges of the relief hole that extend parallel to the direction of moving of recording sheet, or may be jammed because of the shortage of sheet-moving force.